The present invention relates to a discharging roller which discharges a recording medium on which data recording has been performed, a method of manufacturing the discharging roller, and a recording apparatus incorporating the discharging roller.
An ink jet printer that is one of recording apparatuses is generally constituted so as to supply a sheet stored in a sheet feeding tray to a sheet feeding roller, transport the supplied sheet to a recording section while holding between a sheet feeding roller pair, cause a recording head to eject an ink droplet onto the sheet to perform recording, and discharge the sheet to a sheet ejection tray while holding between a discharging roller pair. Since recording on the sheet is thus performed between the discharging roller pair and the feeding roller pair, a rotary speed of the discharging roller is set slight higher than that of the feeding roller to tense the sheet between the discharging roller and the feeding roller, whereby the sheet becomes flat to improve recording accuracy.
FIG. 13A is a perspective view showing a first related-art discharging roller as disclosed in Japanese Patent Publication No. 10-129910A. This discharging roller 1 is formed so that a shaft portion 2 made of plastics becomes longer than at least recordable maximum sheet width, and plural roller portions 3 made of rubber are fitted in the shaft portion 2 with constant intervals. As shown in FIG. 13B, such the discharging roller 1 is formed so that a circular portion of a sectional shape of the shaft portion 2 has diameter Ds and a cross-shaped portion thereof has thickness t, and the diameter Ds must be smaller than diameter Dr of the roller portion 3. Specifically, the diameter Ds is 6.80 mm and the diameter Dr is 11.26 mm. Therefore, the proportion of the outer diameter of the shaft portion to the outer diameter of the roller portion is 60.4%.
FIG. 14 is a section view showing a second related-art discharging roller as disclosed in Japanese Patent Publication No. 10-291874A. This discharging roller comprises a cylindrical body 30 and shaft portions 20 extended from both longitudinal ends of the cylindrical body 30 and having a smaller diameter than that of the cylindrical body 30. The cylindrical body 30 and the shaft portions 20 are made of plastics. The shaft portions respectively have a hollowed portion which are formed by a core 75 or a resin injection port 77. One of the hollowed portion is communicated with a cavity 31 formed inside the cylindrical body 30.
In case that the first related-art discharging roller 1 is formed of synthetic resin, it is necessary to provide thickness deletion (thick removal) so as not to make the discharging roller thick in order to prevent deformation or sink of the shaft caused by internal stress in molding. Therefore, only rigidity of a certain level can be secured. Further, since the rotation speed of the discharging roller 1 is set so as to become higher than that of the feeding roller, power pulled onto the feeding roller side acts on the discharging roller. Therefore, there is anxiety that deformation such as a flexure is produced in the discharging roller 1.
Since the deformation of the discharge roll 1 such as the flexure is restored when a rear end of the sheet is released from the feeding roller pair, there are instances where a so-called flip phenomenon of sheet is produced at this time. In case that an ink jet printer can record data on the whole surface of sheet or the nearly whole surface thereof, recording is continued to the rear end of the sheet even after the rear end of the sheet is released from the feeding roller pair. Therefore, in case that the above flip phenomenon is produced, a bad influence is exerted on recording accuracy.
Regarding the second related-art discharging roller shown in FIG. 14, the sink 34 tends to be produced when auxiliary cavities 40 are filled with the injected resin. This causes deformation or the rigidity reduction of the discharging roller surface. Moreover, if flashes are formed on an outer circumferential surface of the shaft portions 20 and the cylindrical body 30 at the plastic molding process performed by the gas injection method, for example, there is anxiety that the flashes cause sliding load increase of a bearing portion or deterioration of sheet feeding accuracy.